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Moon melding made Titan a chimera

LURKING among the icy moons of Saturn, the giant moon Titan is like a monstrous copy of Earth. Frigid lakes and black dunes made of hydrocarbons lie under a choking atmosphere of organic smog. Now it seems that, like Earth, Titan was built from several smaller bodies smacking together and merging to become a planetary chimera.

The discovery also hints that the creation of Titan spawned icy minions – a family of mid-sized moons unlike anything else in the solar system. The work was presented on 17 October at the annual meeting of the American Astronomical Society’s Division of Planetary Sciences in Reno, Nevada.

Erik Asphaug of the University of California, Santa Cruz, and colleagues think the Saturn system evolved like a planetary nursery, with proto-moons emerging from a disc of ice-rich, orbiting material.

In their model, Saturn starts out with a family of four large moons, similar to Jupiter’s four biggest moons. Computer simulations show that, as these young moons settle into stable orbits, their gravity pulls them towards each other and they go through a series of collisions.

As the final two big moons merge to create Titan, they liberate some icy material from their mantles, which spins outwards and congeals into the mid-size moons seen today.